The US is preparing plans to have two warships on standby in the Black Sea during the Winter Olympics in Sochi.

The warships would be used to evacuate Americans in case of a terror attack or other emergencies, according to government officials quoted in US media.

The US is also looking to have helicopters and other transport aircraft ready in nearby bases, such as Germany, which is about two hours away.

American officials stressed that under the plan, first reported by CNN, the ships or aircraft would be used only in coordination with Russian officials.

Image Caption:Thousands of police will be deployed under Russia's massive security plan

"Air and naval assets, to include two Navy ships in the Black Sea, will be available if requested for all manner of contingencies in support of - and in consultation with - the Russian government," said Pentagon spokesman Rear Admiral John Kirby.

A video posted online claimed responsibility for deadly suicide bombings in the southern city of Volgograd in December and threatened further attacks.

The attacks at Volgograd railway station and on a city tram last month killed 34 people and injured more than 100.

Russian President Vladimir Putin insists the event will be safe. His government has prepared a huge security plan, including 40,000 police officers, to protect Olympic venues and other potential targets.

The State Department has warned Americans planning to attend the Games to be vigilant about their security because of potential terrorist threats.